John Kerry formally reopened the US embassy in Cuba with a flag-raising ceremony on Friday, issuing a call for "genuine democracy" in the country.

It was the first visit to Cuba by a US secretary of state since 1945, and the ceremony at the newly recommissioned US embassy in the Cuban capital marked the return of an American presence to a building the US had vacated in 1961.

"We remain convinced that the people of Cuba would be best served by a genuine democracy," Kerry said.

"For more than half a century, US-Cuba relations have been suspended in the amber of cold war politics," Kerry said. "It's time to unfurl our flags and let the world know we wish each other well."

The secretary of state was welcomed to the country by foreign minister Bruno Rodríguez Parrilla, who dispatched a delegation to attend the ceremony at the seaside facility. Groups of Cuban onlookers, some holding US flags, gathered on adjacent sidewalks and at overlooking windows.